1. Field of Invention
The present invention relates to a heat pump system for a vehicle and a control method thereof. More particularly, the present invention relates to a heat pump system for a vehicle and a control method thereof that improve heating performance and dehumidification performance of the vehicle and prevent frost of an exterior condenser by controlling flow of a refrigerant and increase mileage by minimizing power consumption of a positive temperature coefficient (PTC) heater.
2. Description of Related Art
Generally, an air conditioning system for a vehicle includes an air conditioning module warming or cooling a cabin of the vehicle.
Such an air conditioning module circulates a heat-exchanging medium through a condenser, a receiver drier, an expansion valve, and an evaporator by operation of a compressor. After that, the heat-exchanging medium flows back to the compressor. At this process, the air conditioning module warms up the cabin of the vehicle through heat exchange at the evaporator or cools the cabin of the vehicle through heat exchange with a coolant at a heater.
Meanwhile, energy efficiency and environmental pollution are of increasing concern, and environmentally-friendly vehicles substituting vehicles having an internal combustion engine have been researched. Such environmentally-friendly vehicles include electric vehicles using fuel cell or electricity as power source, or hybrid vehicles driven by an engine and an electric battery.
An air conditioning system of an electric vehicle among the environmentally-friendly vehicle, different from that of a typical vehicle, does not use a separate heater. An air conditioning system applied to an electric vehicle is typically called a heat pump system.
According to the heat pump system, a high temperature/pressure gaseous refrigerant compressed at a compressor is condensed at a condenser and then is supplied to an evaporator passing through a receiver drier and an expansion valve at a cooling mode in the summer. The gaseous refrigerant is evaporated at the evaporator and lowers temperature and humidity of the cabin. However, the heat pump system has characteristics that the high temperature/pressure gaseous refrigerant is used as a heater medium at a warming mode in the winter.
That is, the high temperature/pressure gaseous refrigerant is supplied not to an exterior condenser but to an interior condenser through a valve and is heat-exchanged with an air at the warming mode in the electric vehicle. The heat-exchanged air passes through a positive temperature coefficient (PTC) heater. After that, the air flows into the cabin of the vehicle and raises a cabin temperature of the vehicle.
The high temperature/pressure gaseous refrigerant flowing into the interior condenser is condensed through heat exchange with the air and is flowed out in a state of liquid refrigerant.
According to a conventional heat pump system, the air of a very low temperature or a low temperature is heat-exchanged with the refrigerant at the interior condenser and the refrigerant of a very low temperature is flowed from the interior condenser to the exterior condenser in the winter. Since a surface of the exterior condenser is frozen, heat-exchanging efficiency and heating performance and efficiency of the heat-exchanging medium may be deteriorated. In addition, since humidity becomes high due to a condensed water remaining at an exterior of the evaporator in a case that a conversion from the cooling mode to the warming mode occurs, moisture condenses on a vehicle window and dehumidification performance may be deteriorated.
To solve such problems, the compressor stops operating and warming is performed only by the PTC heater at a defrosting mode where a surface of the exterior condenser is defrosted. Therefore, heating performance may be seriously deteriorated, heating load may be increased due to increase of power consumption, and mileage may be shortened at a driving with warming.
In addition, since heat for converting a liquid refrigerant into the gaseous refrigerant is insufficient when the liquid refrigerant flows into the from the interior condenser, compress efficiency may be deteriorated, heating performance may be seriously deteriorated when an air temperature is low, the system may be unstable, and durability of the compressor may be deteriorated when the liquid refrigerant flows into the compressor.
In addition, noise and vibration may occur due to frequent open/close operation of a 2-way valve at a dehumidification mode where moisture is removed from the cabin of the vehicle.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.